This section provides background information related to the present disclosure which is not necessarily prior art. It is often beneficial to monitor the condition of filter elements. One of the most common ways to monitor the condition of filter elements is to measure a difference in pressure across a filter vessel using a differential pressure gauge. The measurable difference in pressure occurs over time because, in a clean filter, a fluid flows freely without restriction, and in a filter filled with dirt and debris, the fluid flow is restricted, thus resulting in an increased pressure drop as the fluid flows through the filter vessel.
Various types of differential pressure gauges are available. For example, a pressure gauge including a piston may be used to measure the difference in pressure. Using such a device, the motion of a close fitting piston is balanced by a spring and is observed in a housing disposed around the piston and forming a piston chamber. A higher filter inlet pressure is applied to a side of the piston not connected to the spring, and a lower filter outlet pressure is applied to a side of the piston connected to the spring. As the difference in pressure becomes greater, the piston moves to compress the spring until the total force on one side of the piston is equal to the total force on the other side of the piston. As a result, a position of the piston indicates the differential pressure across the filter vessel.
The position of the piston may be determined in various ways. The housing may be transparent, allowing a user to actually see the position of the piston, or a sensor may be used to sense the position of the piston. Such a sensor may be a magnetic sensor. However, disadvantages of using the magnetic sensor include expensive materials, increased errors in differential pressure readings due to damage or hindrance from the presence of contaminants between the piston and the housing, numerous components, and increased interference.
It would be desirable to have a differential pressure gauge that is inexpensive to make, and that uses a rotating positional element located remote from the piston that minimizes interference, friction, and errors, is highly reliable, and does not attract contaminants to the piston.